copra dryers and copra drying technologies by dr. … · 2018. 3. 20. · copra dryers and copra...

COPRA DRYERS AND COPRA DRYING TECHNOLOGIES

by

Dr. Klaus Dippon1 and Engr. Rose VillarueP

ABSTRACT

T h is p a p e r b r ie f ly d is c u s s e s th e b a s ic p r in c ip le s o f d ry in g c o c o n u ts fo llo w e d b y th e f in d in g s o f th e p e r fo rm a n c e e v a lu a t io n o n e x is t in g d ry e rs

(T a p a h a n D ry e r , M o d if ie d K u k u m D ry e r, U P L B D ry e r) in th e P h il ip p in e s

a n d th e d e v e lo p m e n t o f n e w c o c o n u t d ry e rs . T h e r e s u l ts r e f le c t th e ir

p e r fo rm a n c e re g a rd in g the u n ifo rm ity o f d ry in g , la b o r r e q u ire m e n ts a n d the

q u a li ty p ro d u c e d . A se rie s o f d ry in g tria ls w a s c a rr ie d o u t to d e te rm in e th e ir

m a in a d v a n ta g e s a n d d is a d v a n ta g e s . B a s e d o n th e r e s u l ts a n d a d d it io n a l

in fo rm a tio n o n th e p e rc e p tio n on w h a t a c o c o n u t d ry e r s h o u ld b e , a se t o f

c r i te r ia w a s e s ta b lish e d . S in c e th e re w as n o d ry e r a m o n g th e te s te d w h ich

c o u ld m e e t th e s e c r i te r ia , a n ew in d ire c t d ry e r a n d a s o la r d r y e r w e re

d e v e lo p e d a n d te s te d . T h e p a p e r a lso d e s c r ib e s th e m a in fe a tu re s o f th e se

d ry e rs a n d th e re su lts o f th e te s tin g d o n e so far.

1. Introduction

D rie d c o c o n u t m e a t (C o c o s n u c if e ra L .) is c a lle d c o p ra . In c o u n tr ie s

lik e th e P h ilip p in e s und In d o n e s ia th e c o c o n u t tree p la y s an im p o r ta n t ro le in

th e e c o n o m y . A c c o rd in g to th e la te s t s ta t is t ic s th e c o c o n u t in d u s try in th e

P h ilip p in e s c o n tr ib u te s a b o u tU S S 971 m illio n to th e n a tio n a l e x p o r ts ( a b o u t 7

% (1 9 9 0 ) o f th e to ta l m e rc h a n d is e e x p o rts ) . A b o u t 8 0 % o f th e p ro d u c tio n is

e x p o r te d m a in ly as c o c o n u t o il (C N O ) a n d c a k e . T h e a m o u n t o f c o p ra

e x p o r te d is s te a d ily d e c re a s in g an d a c c o u n te d fo r 35 0 0 0 M T in 1995 . 1 2

1 Post Harvest Consultant GTZ (Deutsche Gesselschaflfur Technische Zusammenarheit nibH; German Agency fo r technical Cooperation)

2 Project Development Officer 111, 1C A (Philippine Coconut Authority) and Counterpart fo rGTZ Postharvest Consultant

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The oil is used as raw material for industrial products and food. C opra cake is part

o f animal feed com pounds. It is known, that improperly dried coconut m eat will result

in a bad quality. Aside from high contents o f free fatty acids (ffa) and bad color, molds

p roducing aflatoxin will grow if drying is not brought dow n to a safe m oisture content

level. Properly dried coconuts will result in aflatoxin free copra.

In most cases, copra produced in the Philippines is o f inferior quality e g. high ffa,

aflatoxin and m oisture content, bad color and odor. The oil derived therefrom is also o f

po o r quality and needs additional refining to meet international standards. Poor quality

is subject to an autom atic price deduction o f 10 to 15% in the world m arket, thus

resulting in annual losses o f m ore than US$ 40 mill. As long as no quality based pricing

system is introduced and applied, farmers will continue producing poor quality copra.

They can not be blamed for the existing situation, since their behavior is ju st rational.

P roducing good quality copra, e.g. white in color, low ffa content and aflatoxin free

reduces their income since copra is paid according to weight.

2. B asic P rinc ip les o f C o c o n u t D ry ing

M ost o f w hat is discussed in the next paragraphs can be applied to all coconut

dryers no m atter where they are used and how they look like.

Drying can be described as a process, wherein w ater is dislodged and evaporated.

Even under ambient conditions, evaporation will take place as long as the actual m oisture

conten t o f the product is above its equilibrium m oisture content (EM C). The EM C is

determ ined by the properties o f the product, tem perature, humidity and the pressure o f

the ambient air. At this point the weight o f the product does not change anymore. Under

the prevailing weather conditions in the Philippines the EM C for copra stands at 6 to 7%.

This means that drying down to a lower m oisture content is w asting time and money,

since copra will absorb w ater until the EM C is reached.

Drying starts with the evaporation o f surface w ater followed by the diffusion o f

m oistu re from inner layers tow ards the surface. As long as the m oisture migration is

higher than the evaporation on the surface, the rate o f drying will remain constant.

Evaporation, i.e. the rate o f drying, is mainly affected by tem perature and humidity o f the

drying air. Quality requirem ents on the product determ ine the highest drying air

tem peratu re possible. Humidity, tem perature and ambient pressure define the w ater

holding capacity o f air. Table 1 shows the effect o f changes in tem perature and humidity

on the water holding capacity at two different locations. Since the drying air pressure can

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be considered constant, while drying coconuts in natural draught dryers, table 1 is based

on a constant air pressure o f 1 bar.

Table 1: Water holding capacity of air

» ) t ro p ic a l c o u n try ( x - 2 1 . 9 g V g d ry a ir at 3 0 °C and 8 0 % )

temperaturem

humidity1*1

max. water absorption [g/k* dry air)

AX

[fcVg dry air]

30 80 22.9 1 . 0

40 46 26.4 4.5

50 29 29.6 7.7

«U B « S 3 * 1MK3B70 10.9 36 2 14,3

80 6.5 39.6 17.7

90 4.1 43.6 217

100 3.0 46.4 24 5

h) mediterranean country (x-8.2 ft/Wg dry air »1 30**C nx) 30%)

temperaturer o

humidity1*1

max. water absorption

AX

[g/Vgiyair)

30 30 1 5J 7.1

40 18.3 15.9 7.7

Maai«>aaiaB& llgjjS^ jBSoM60 6.9 22.0 13.8

70 4 6 249 16 7

80 3.4 28.1 19.9

90 2.6 31.4 23.2

KM) 2 1 34 9 26 7

T he rate o f drying at a given tem perature and hum idity is fastest right after

splitting the coconuts. The lower the m oisture content the m ore difficult it gets to further

dry dow n F ig u re 1 show s a drying curve (time is plotted against m oisture conten t) for

coconut meat at a drying tem perature o f 95°C. In this case 2.5 hours are needed to bring

dow n the moisture content from 45% to 35%. In contrast, 8.5 hours are needed to dry the

coconut meat from 20% dow n to 10%, or m ore than three tim es longer. Drying dow n to

a m o istu re content that is still accepted by the buyer is the logical consequence o f this

drying curve even if a price deduction is applied for high m oisture content.

Evaporation has to be followed by the removal o f the m oisture from the pile This

requires a certain air velocity to transport the evaporated w ater to the outside.

As far as a coconut dryer is concerned the m ost im portant factors affecting the

perform ance o f a dryer are:

o properties o f the product (size, age, initial m oisture content, etc.)o dry ing m anagem ent (nuts arrangem ent, pile height, time lag from splitting to start

o f drying)o physical properties o f the drying air (humidity, tem perature and velocity)

N either size, age nor initial m oisture content are constant. The average diam eter

o f nu ts o f different varieties may vary from 10 to 20 cm. The higher the difference in

d iam eter in a batch, the higher the percentage o f overlapped nuts, thus resulting in a

higher percentage o f wet copra. Y oung nuts (less than 11 m onths old) are m ore difficult

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to dry than old, m ature nuts (13 to 14 m onths old). I f the nuts are not properly drained

after splitting and/or splitting and loading is done on a rainy day, m ore w ater has to be

evapora ted . In this case the drying time has to be extended thus resulting in a lower

efficiency.

Based on drying trials, the arrangem ent o f the nuts is not significantly affecting

the quality o f the copra, hence arranging the nuts (first layer facing up and all o ther layers

facing down) will require additional four hours per 2000 nuts.

The higher the pile o f coconuts loaded, the m ore difficult it is for the drying air

to pass through the nuts. This will be reflected in a m ore uneven drying o f bottom and top

layer. Form er will be overdried while the top layer still has a high m oisture content.

T here are no specific data in the literature on the optim um bed height. D as [1]

recommends a bed height o f 20 - 30 cm; Lozada [2] 45 cm and Ly, Tung and Edilberto

A. Hinay 50 cm [3],

Similar to the bed height a wide range o f tem peratures are m entioned in the

lite ra tu re . Q uite often the authors recom mend a two stage drying. A high tem perature

initial stage is followed by a period o f lower tem perature. According to W oodroo f [4] a

temperature o f 66°C for the first 8 hours followed by 60°C until drying is finished. Trials

done by G uarte [5] revealed that even tem peratures o f 90°C are acceptable, since the

quality is slightly affected. H ence Lozada et al recom m ends [6] a drying tem perature o f

35°C to 50°C for the first 16 hours o f drying followed by 50°C to 55°C during the next

phase until a final m oisture content o f 8 to 10 % is reached.

Muhlbauer, Kellert and Guarte [5] stated, that an increase in air velocity from 0.1

m /s to 1.0 m /s will reduce the drying time by 48% for a final m oisture content o f 7 %.

According to Dum aluan and Lozada [7] drying rates w ere not greatly influenced by the

air flow rate.

Since the average air flow rate in natural draught dryers is below 1.0 m/s,

additional blow ers are needed to achieve higher velocities.

Loading should be done right after splitting (after the w ater is drained off). Drying

trials have shown a slight discoloration o f nuts loaded m ore than four hours after

splitting. The m ore drying is delayed the higher the percentage o f discoloration.

Coconut dryers can be characterized by the classification given in Figure 2.

Since copra is considered as a low value product, sophisticated dryers are not a

necessity. Even the use o f ventilators for a more constant air flow can not be

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recom m ended due to econom ic reasons. W hat is left are natural d raft dryers (d irect and

ind irect), sun and solar dryers. This classification is applicable to m ost o f the coconut

producing countries.

Dryers wherein the com bustion gases com e in contact w ith the coconut m eat are

classified as d irec t d ryers. W henever heat exchangers are used to heat up am bient air for

drying purposes, the dryer is considered in d irec t.

T he sun is the source o f energy for both sun d ry in g and so la r d ry in g . The

d iffe rence is that a structure (very simple to high sophisticated) is used to enhance the

effect o f the insulation. In simple w ords solar dryers can be considered as m edium to trap

the sun’s heat.

3. D e te rm in a tio n o f W o rk in g P e rfo rm a n c e o f D ry ers

3.1 Dryers in l /se

A series o f tests w ere carried out in o rder to get enough data for a thorough

evaluation o f the dryers used in the Philippines.

3.1.1 Tapahan Dryer

This dryer is one o f the com m only used direct dryers in the Philippines. It com es

in different versions, starting with an open pit filled w ith husks and covered by a bam boo floo ring up to m ore advanced dryers w here the drying platform is provided w ith a wall

(hollow blocks, plywood, etc.) In F igure 3 the main com ponents and the air/heat flow are shown. The capacity o f a standard tapahan dryer is 2000 nuts (volum e o f drying bed: 2.69 m3)

3.1 .2 UP LB D ryer

The body o f the UPLB Dryer is cubical in form m easuring 1.91 m in length, 1.83

m in w idth and 1.77 m in height. Lum ber m easuring 1.5“ x 2" and 1.5“ *x 1“ is used for

the basic structure. The w ooden structu re is lined w ith G I-sheet to form drying bed and heating chamber. At the front side a swinging door and tw o trails allow the placem ent o f one burner inside at a tim e (see F ig u re 4). A heat decipato r (m ade o f G I-sheet) betw een

burner and drying bed is provided to give an uniform tem perature distribution. Four air

inlets (18 x 8 cm), located at each side betw een drying bed and G I-Sheet, allow a steady

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air flow, essential for convectional drying. The dryer has a capacity o f about 1000 nuts

(volum e o f drying bed: 1.47 m3).

3.1.3 M odified Kukum D ryer

The m odified Kukum D ryer is an indirect natural draught dryer m easuring 1.83

m in w idth , 3.66 m in length and 2.13 m in height (see F ig u re 5). A bout 2000 nuts

(average size) can be accom m odated (volum e o f drying bed: 2.8 m3). Its heat exchanger

is m ade up o f three standard oil drum s welded together with five sem i-circular baffles installed alternately inside the drum s at distance o f 0.46 m. The furnace m easures three feet in length and tw o feet in width and is made o f steel plastered with 6 cm thick

cem ent-ash m ixture inside. The furnace is provided with a slanting grate and door to

regulate air entry. A butterfly valve is also provided at the chimney to control the tem perature.

3.1.4 Sun Drying

D rying trials w ere done in connection with the perform ance evaluation o f solar

dryers. The splitted nuts were exposed on a pavem ent and slightly tilted area to allow the

w ater to drain off.

3.2 Data Gathering

Table 2 contains all sensors, their accuracy and location used for the perform ance evaluation. These sensors are connected to a com puter based data acquisition system. Program m ed softw are is used for collecting the data in 6 minutes intervals from each sensor. The value saved to the hard disk is actually the mean taken from 20 readings at each sensor every 6 minutes. This is necessary to keep the effect o f voltage and frequency fluctuation on the actual reading at a minimum level. The analog signals are converted

into digital signals and then transm itted to the com puter via A /D -converters (see F igu re

6). Up to 26 tem perature, nine humidity and four w eather data sensors w ere used.

The samples for the initial m oisture content w ere taken after loading the dryer. A special scooping tool w as used to cut o ff small pieces from 20 nuts taken randomly

from the whole batch. A nother 10 nuts were taken from the batch o f splitted nuts to determ ine the initial meat to shell ratio.

In order to monitor the reduction in m oisture content at different locations during

the trial, nine baskets (UPLB dryer: 5 baskets) w ere placed inside the drying bed. Each basket was divided into three layers (top, middle and bottom layer) with '/2" welded wire. Weighing was done every tw o to four hours. W ith this setup, a detailed description o f the drying process within the drying bed in different layers could be given.

The final m oisture content o f the whole batch o f copra w ere determ ined by

getting a segment o f copra from top to bottom from all representative points o f the

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dryer. The sam ples w ere then scooped and mixed thoroughly. Five kilos o f copra w ere then taken and knife milled for qualitative analyses, i.e., m oisture conten t, ffa content,

oil color, oil conten t and aflatoxin content.

C o p ra grading (visual inspection) w as done im m ediately after unloading and

scooping based on m oisture content, insect attacks and mold grow th. In som e trials about

10 kg copra w ere taken from the batch sample after scooping for four w eeks storage

befo re being visually inspected. Part o f this sam ples (5 kg) w ere taken for qualitative

analyses.

3.3 Results

3.3.1 T apahan D ryer

The results have shown a fairly distributed tem peratu re within the drying bed. An

average tem pera tu re o f 86, 95 and 88°C w as m easured from front m iddle and back

section, respectively. The tem perature w as fluctuating which is reflected in a high

s tan d ard deviation (see Table 3). H igher tem peratures in the m iddle section are caused

by the fuel concentration at the middle. The higher tem peratu re in the m iddle section is

also reflected in a low er m oisture conten t in this area. D uring the testing the following

fuel feed rate w ere used: first firing: 40 husks, after 35 m inutes another 25 husks followed

by 15 husks per 15 m inutes until drying is finished. There is no tem peratu re controlling

device except a change in the fuel feed rate. A higher fuel feed rate as m entioned is not

recom m endable because the risk o f burning the dryer and copra is high.

Quite often scorched copra w as found in the bottom layer, w hile the m iddle layer

w as be tte r in color. Parts o f the top layer still had w et nuts, especially at the front and

back.

Since the fuel (husks) is burned inside a pit underneath the drying bed, the dryer

has to be attended to w hen in operation to prevent the dryer from burning.

On average, about 20 hours firing are needed to reach a final m oisture content o f

about 10 % (see F ig u re 7). This means, that in m ost cases drying has to be done on tw o

days. Contrary to the claims o f users, it is not possible to bring dow n the m oisture content

to 10% in 16 hours w ithout having lots o f scorched copra o r higher share o f w et copra.

For the 2000 nuts capacity Tapahan dryer a w orking tim e o f 6.9 m inutes w as com puted

to p roduce one kilo copra.

Based on a firing time o f 20 hours, the am ount o f energy consum ed (input) stood

at a round 94 kW h. The ratio betw een ou tput (evaporated w ater) and input is called

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thermal efficiency. It is betw een 12 and 13% at a specific energy consum ption o f 19 MJ

per kg evaporated water.

Sm oke drying is also known as source o f PA Hs (polycyclic arom atic

hydrocarbons). Results o f Tapahan dried copra showed figures as high as 79.8 pg/kg [8],

The advan tage o f sm oke drying is its effect on the storage (quality) because o f the

preservative properties o f smoke. Less aflatoxin producing m olds will grow.

3.3.2 UPLB Dryer

The tem perature in the bottom layer w as fluctuating and uneven (see table 4). In

some locations a maximum temperature o f m ore than 180°C w as recorded, but the center

show ed a relatively low tem perature. Even after seven burners (m ore than 20 hours

drying), the center portion in the drying bed w as still wet (see Figure 8), while the nuts

in the bottom layer in other locations o f the drying bed were scorched.

The average fuel capacity (cracked coconut shells) per burner is 15 kgs. It takes

2.5 to 3.3 hours to consum e one burner. For this dryer the w orking time (including

dehusking and splitting) to produce one kilo copra was com puted at 5.44 minutes. About

24% o f this time is needed to break the shells used as fuel.

The thermal efficiency o f 24.5% was measured at a specific energy consum ption

o f less than 10 MJ per kg evaporated water.

The average PAH content was measured at 60.7 pg/kg [8],

Since the dryer is collapsible, it can easily be transferred to another location.

3.3.3 M odified Kukum Dryer

T em perature is quite even between left, middle and right side. The lengthwise

distribution is m ore uneven. Highest tem peratures w ere m easured at the front section,

while lowest at the back (see Table 5). The difference in tem perature betw een front and

back section o f the drying bed is about 20 to 25 Kelvin. Cold spots w ere observed at the

back section within the top layer. The fuel feed rate used in operating the Kukum dryer

was betw een 6 and 10 husks per 10 minutes. How ever, a higher fuel feed rate w as used

for the initial stage (first drying day).

A bout 30 hours are needed to dry one batch down to less than 10%. Based on a

10 hours operation time per day, drying will take three days (see Figure 9). About 8.7 minutes are needed to produce one kilo copra with the modified Kukum dryer.

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As far as copra quality is concerned, this dryer show ed the best results am ong the

tested dryers. However, maintenance and repair costs are the highest. They are attributed

by the m etal parts o f the dryer which start to co rrode as soon as the dryer is being

co n stru c ted . Frequent use o f the dryer will reduce corrosion, but never stop it. Since

copra is a low value product, the use o f stainless steel or even the application o f prim er

m akes no sense. The exposure to high tem peratures, aggressive fum es and w ater will

induct corrosion.

Similar to the tapahan dryer, a therm al efficiency o f 12.7% w as com puted at a

specific energy consum ption o f 19 M J per kg evaporated w ater.

4. D evelopm en t o f C o c o n u t D ryers

Within the Philippine German C oconut Project, a solar and an indirect dryer w ere

developed and tested. Form er is designed to cope with the drying needs o f individual

c o co n u t farm ers (2 to 5 has which equal to about 10000 to 25000 nuts/year) while the

later is mainly designed for coconut grow ing cooperatives and /or bigger plantations. One

unit o f this dryer is sufficient for about 40 ha o f coconuts.

4.1 Development o f Indirect Dryer

T he o u tpu t o f about 80 drying trials on different dryers as well as additional

in form ation from farm ers m eetings, visits o f farm ers to the pro ject and personal

experience on w hat a coconut dryer should be, lead to the form ulation o f different

criteria. T hese are: 1 2 3 4 5

1. w orking perform ance

2. durability

3. ease o f operation

4. costs

5. ease o f construction

The minimum requirem ents on the w orking perform ance are as follows:

o not m ore than tw o drying days

o less than 10% final m oisture content and uniform dried

o less than 20 ppb aflatoxin content

o fuel usage low er than 90% o f the husks o f nuts loaded

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The lifespan o f the essential dryer com ponents should be at least five years. Construction

should not require any special tools and the total costs should not be higher than any

alternative indirect dryer.

Since none o f the tested dryers met these criteria, we decided to develop a new

indirect dryer. Due to the disadvantages o f direct dryers like soot (PA H ) contam ination

and scorched copra, we decided in the early stage o f our research to go for indirect

dryers. Table 6 contains the grading o f different dryers including the newly developed.

Preliminary trials w ith bricks as heat exchanger show ed a promising potential to

replace the metal. Bricks are know n for their high strength (fire and w eather resistance),

durability (long service life) and dimensional stability.

Several prototypes were constructed to optim ize shape and size o f the burner and

to determine the appropriate thickness o f the bricks. The final version o f this brick dryer

is called COCOPUGON (see in Figure 10)

The dimensions o f the dryer are set to 260 cm in width, 360 cm in length and 200

cm in height. Standard fire bricks and 2.5" crow n bricks w ere the m aterials used for the

chimney and the heat exchanger, respectively. The dryer can accom m odate 2500 average

sized nuts per batch (volum e o f drying bed: 3.33 m3). To facilitate ease o f loading and

unloading, the right side o f the drying bed wall is removable. A one step stair and

platform is also provided on the same location.

Unlike dryers with metal heat exchangers, preheating is needed for this dryer.

Firing should be done first before loading the splitted nuts. The burner can accom m odate

about 200 to 300 husks. Refuelling has to be done every 3 to 5 hours. The heat stored in

the bricks will be released slowly after the last firing on the first drying day, such that

drying will continue for several hours w ithout adding fuel (husks).

Figure 11 shows the average drying and burner tem perature for one specific trial

(first day five firings, second day three firings). The last firing on the first drying day was

at 2 1 :00. W hen fuel was added next morning (7:00) the tem perature still stood at 52°C.

The slope o f the line added to Figure 11 indicates the increase in tem perature per time

interval.

The equation for the slope o f the line is: y = 30.0 + 6.6 x

After a preheating time o f 3.5 hours and a loading time o f tw o hours, the average

tem pera tu re in the bottom layer is 66.3°C. The burner then has to be fed five to seven

tim es for the whole drying period. Form er could be accom plished in only one day at a

feeding interval o f about three to four hours at a constant fuel feed rate. Unloading could

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be done a fte r the dryer has cooled dow n on the second day. I f operated on a tw o days

schedule, five firings are needed on the first day and another tw o to three firings on the

second day. U nloading will be done the next m orning to utilize the heat stored in the

b ricks. I f the baffle in the chim ney is closed during night time, em ber can still be found

inside the burner on the following m orning m aking it easy to continue firing. The

tem p era tu re curve for the burner has several small peaks indicating the maximum

tem peratu re per feeding interval. The effect on the drying bed tem perature is minimal,

thus having an almost constant drying tem perature. Even if the burner is fully loaded, the

resulting tem perature in the drying bed w ont exceed 90 to 95°C, thus elim inating the risk

o f producing scorched copra.

S ince the heat exchanger or the burner cover alm ost the w hole area inside the

d ry er body, the tem peratu re distribution is very uniform. The difference in tem perature

betw een the highest and low est value is less than 5 Kelvin. A standard deviation o f 3

Kelvin indicates a very constant tem perature (see F ig u re 12 and Table 7).

D uring operation , the dryer opera to r spends tw o hours per batch at the dryer,

m eaning the labor requirem ents w ere cut dow n by m ore than 50 % to 4 1 m inutes per

k ilogram copra com pared with the modified Kukum dryer. T he o pera to r can leave the

dryer in betw een fuel feedings and use his time for o ther activities.

The thermal efficiency w as very constant with an average o f about 15% resulting

in a specific energy consum ption o f about 17 MJ per kg w ater..

T he drying cost per kg o f copra (see table 8) w as determ ined to be 2 .6 C ents

(Pesos: 0.66).

The copra quality w as found to be far better than the minimum requirem ents set

for good quality copra for dom estic use, i.e., 14% m oisture content, 5% free fatty acid

con ten t o f oil (as lauric); 10% mold infection; and 20 ppb aflatoxin content. The color

o f oil is not m uch o f concern, how ever, a 9 red and 50 yellow co lor is required for

ex p o rt o r m erchantable quality. The quality o f copra produced also met the criteria set

for the dryer. G ood quality copra production w as attributed to the appropriate procedure

o f drying, i.e., fast; sm oke-free, and proper tem peratures. Brow nish copra w as produced

from th e b o tto m layer. This is due to higher tem perature exposure for a longer period

D ue to delayed drying som e brow n colored copra w as also produced from the top layer

On average, about 80% per batch was white. About 1% o f the total copra produced was

w et at optim um drying set up. The average ffa content o f m ore than 20 drying trials

s to o d at 0.21 (Oil color: 0.55 red; 2.75 yellow (Lovibond)). A verage fuel consum ption

is about 80% o f the husks from the total nuts loaded

89

Solar dryers make use o f an effect, which is similar to the well known

greenhouse effect. Figure 13 contains all essential com ponents to describe energy flow

in solar dryers. Com pared with sun drying, solar dryers can generate higher air

temperatures at a lower relative humidity which both conducive to improved drying rates

and lower final moisture contents [9]. In addition, the negative effects o f rainfall, insects,

dust and molds on the quality o f copra produced by sun drying can be minimized.

The basic criterion for the developm ent o f a solar dryer was to provide the small

coconu t farm er an alternative to sun drying at the lowest cost possible. Therefore the

d ryer has to be transportable and small while utilizing locally available m aterials and

keep ing the labor requirem ent for coconut drying lesser than sun drying.

At the start o f the project the potential o f solar dryers for coconuts was proven and

consequently further developed. Based on the findings o f these initial trials, several

designs using different materials w ere build, tested and analyzed. Since the results were

quite similar, the main criterion for selecting the best dryer was to minimize farmers

expenses. The cost is lowest for a bam boo based design. The price per square m eter is

less than US$ 0.75. For rattaiVbamboo, rattan and w ater pipe designs the costs are US$

1.8, 2.3 and 6.9, respectively.

The bamboo type solar dryer is shown in Figure 14. A com plete bill o f materials

can be found in table 9. The main parts are the bam boo frame and the plastic sheet. At

a length o f 3 m and a width o f 1.75 m, an area o f about 5.25 m2 is covered - enough to dry

200 - 250 nuts per batch. Farm ers can easily make their own dryers since bam boo poles

are available throughout the country. They only need a hand saw, nails or w ood glue and

the plastic sheet for the construction. The plastic sheet is the most essential part o f the

dryer thus requiring a careful selection.

In general the following standards for plastic sheets used as cover in solar dryers

should be followed: 1

1 life span: minimum two years (U V -protection needed)

2: gauge: min. 0.004 (0.10 mm)

3: width: min. 50" (tube type)

4: Transparency: min. 80 %

5: Price: less than 1 US $ per m2.

6: ecologically friendly

4.2. Development o f a Solar Dryer

90

Since PV C (Poly-V inyl-C hloride) is expensive and not environm ent friendly

(so ttin g agents and dioxin are em itted w hen disposed), PE (Poly-E thylene) w as chosen

because o f its low price and availability th roughout the country. O thers like PTFE

(Poly-T etra-F lour-E thylene) w ould give the best optical and m echanical properties, but

until now not produced in the Philippines.

In o rder to get a life span o f at least tw o years, the plastic sheet has to be UV-

stabilized, m eaning light stabilizers are added to prevent photo-oxidative damage.

U nprotected plastic sheets will be destroyed within w eeks depending on the region and

level o f solar radiation.

F o r th e solar dryer a blend o f L L D PE (linear low density PS) and L D PE (low

density PS) at a ratio o f 40: 60 w as used. M ixing these tw o m aterials will result in a

higher tensile strength and tear dilation. Table 10 contains the m ost im portant properties

o f these tw o m aterials. T he sheet w as extruded in D avao, Philippines, w ith the

specification o f a life span not less than tw o years

W ith this sheet attached to different designs, a series o f drying trials w ere

conducted to com pare sun and solar drying. W eather data (rainfall, tem perature,

humidity, wind speed and radiation), tem peratures and hum idities inside the solar dryers

as well as copra quality related param eters w ere recorded and analyzed. The dryer is

operated in such a way that after splitting, the nuts are spread on the ground and covered

with the dryer. Since the dryer weighs less than 20 kgs, one w orker can do the job. Once

the nuts are covered, the next w ork that has to be done are unloading and scooping. The

results are as follows:

Com pared to sun drying, a maximum tem perature o f up to 65 °C can be reached

in the solar dryer during noon time, about 30 Kelvin m ore than the am bient tem perature

(see F ig u re 15). H ow ever, drying time for sun dried coconuts under optim um w eather

conditions is slightly longer, because the uncovered coconut m eat also absorbs the solar

radiation, thus increasing m eat tem perature which in turn accelerates drying. The results

show , that the difference in average m eat tem perature betw een solar and sun dried

coconuts on sunny days w as in the range o f only 3 to 6 Kelvin.

On average, drying time is cut down by about 2 days to 4.5 days w hen using solar

dryers (see F igure 16). This is the result o f com parative drying trials done for about half

year. However, having three to four straight sunny days w ithout rainfall, sun drying could

be finished in alm ost the sam e time.

91

The average radiation per day was m easured at 5.1 kW h/m 2. Based on an average

drying time o f 4.5 days about 23.4 kW h/m 2 are needed to bring the m oisture content

d o w n to lO % .

Drying trials done throughout the year showed that the color o f alm ost 50% o f the

solar dried coconuts were white after reaching the final m oisture content o f less than 10%

com pared to 18% o f sim ultaneously sun dried coconuts while about 71% w ere moldy.

To obtain good quality copra, the first drying day should be sunny. U nder w eather

conditions favorable for the grow th o f aflatoxin producing molds, the average aflatoxin

content in solar dried coconuts w as 1/10th o f sun dried coconuts. Form er w as about 10

ppb while the later resulted in aflatoxin content o f m ore than 100 ppb. Solar drying will

reduce the red color and ffa content by 28% and 32% , respectively.

Front and back side have to be kept open to allow a steady air flow to rem ove the

m oisture from inside. The dryer should be aligned to the main wind direction to

maximize air flow. U nder the existing w eather conditions at the D avao Research Center

(Southern Mindanao) the theoretical w ater absorption capacity o f this dryer is about 100

kg per day. Assuming a drying time o f 4.5 days and a load o f 100 kg coconuts (meat-shell

ratio: 1.8) to be dried dow n from a m oisture content o f 50 to 10%, about 6.6 kg w ater

have to be evaporated per day. This indicates, that even in areas with a low er air velocity

the dryer can be used.

R attan is not as durable as bamboo. That is why only good bam boo should be

used as material for the frame. The attachm ent o f the plastic sheet is done with nails

cushioned with canvas (tarpaulin). So far no problems w ere noticed except the attachm ent

with double seamed loops where the plastic w as torn apart along the seams after five to

six months. After less than a year some o f the joints m ade o f splice rattan w ere broken.

If bamboo is used, holes can be drilled in the poles to fit in the ends o f the arc. The joints

should be sealed with w ood glue.

Since the half cups are usually turned upside down in the evening or when rain

is anticipated, m ore labor is required for sun drying.

Except grass, any surface can be used as long as the underground is slightly tilted

to prevent w ater accum ulation inside the dryer. Animals should be kept away from the

dryers, since the plastic sheet can be easily destroyed by stepping on it.

When placed on a clean surface or paved area, the cost for drying (Bam boo type)

w ere determ ined to be US $ 0.014 per kilogram copra (as o f 5/95). The assum ption for

this calculation are listed in table 11.

92

The average form size o f three hectares needs tw o solar dryers to dry the coconut

p ro d u ce annually. This will cost the farm er less than USS 30. T o m aintain a good

perform ance the plastic sheet should be cleaned occasionally and replaced every tw o

years, approximately. A new sheet will cost about U S$ 3 per dryer. R eplacem ent can be

easily done by the farm ers them selves.

Aside from coconuts, the dryer can also be utilized fo r drying o ther p roducts like

m ango, rice etc.

93

33rd COCOTI-CII Meeting, July I 5 -19. 19%. Kuala Lumpur. Malaysia

Drying Time [h]Figure 1: D r y i n g C u r v e

Standard Ceylon Kiln

Improved Ceylon Kiln

Malaysian Kiln Tapahan Dryer

Tapahan de Vapor Dryer

WSTEC Dryer UPLB Dryer

Marschallese Dryer

Indirect Drying

[natural draught] forced air

Modified Kukum Dryer

Cocopugon

Village Copra Dryer (Western Samoa)

Figure 2: C o c o n u t d r y e r c l a s s i f i c a t i o n

Coconut Dryer and Drying Technologies

94

33rd COCOTECH Meeting, July 15-19, 1996, Kuala Lumpur, Malaysia

ft ambient air

Figure 3: Tapahan Dryer

F ro n t View Side View

Figure 4; UPLB Dryer


95

33rd COCOTP.CII Meeting, July 15-19. 19%, Kuala Lumpur, Malaysia

Table 2: M easuring equipm ent for dryer testing

Location Measurement Device Manufacturer Accuracy Range

drye r w eigh t digital A & 1) 50g 0 . . I 5 0 kg

ba lances Satori us lg 0.. 12 kg

d ry e r l im e triple t im er - - -

d rye r tem pera tu re C u /C u-N i

T h e rm o

coup les

ROssel + /- 0 .5 °C -2 0 0 . .3 5 0 °C

w e a th e r sta tion rel. hum id i ty hum id i ty

transm it te r

E + E E lec tron ic + /- 2 % 0 . . I 0 0 %

w e a th e r sta tion tem pera tu re PTIOO T h ic s 0.1 °C a t 0 °C -3 0 . .8 0 °C

w e a th e r s ta t ion w in d speed a n em o m ete r T hies - 0 .5 . .35 m /s

w e a th e r sta tion g loba l radia t ion p y ra n o m e lc r K ip p und Z o n en m ax. 0 . .4 0 0 0 W/m* +/- 2 %

Note: The weather station is composed of several measuring instruments that arc attached to a computer in a nearby data monitoring center (the "Hohenheim Container") which could automatically record data both on ambient conditions and other set-ups.


96


0 5 10 15 20 25 30firing time [h]

Trial 22

T ria l 23

x

Trial 24

v

Trial 26

A v g .

Figure 7: Drying curve tapahan dryer

Table 3: Average temperature and sd in bottom layer o f tapahan dryer

avg.Temperatures

right middle left

bottom sd bottom sd bottom sd

front 86.6 19.1 86.9 18.8 84.9 17.0

middle 93.1 21.7 98.3 21.5 93.1 20.4

back 87.5 17.4 89.4 20.6 86.1 17.9

Table 4: Average temperature and sd in bottom layer o f UPLB dryer

avg.Temperatures

right middle left


front 105.4 22.4 103.8 25.1 115.8 28.1

middle 90.7 20.1 80.1 18.2 112.5 26.7

back 106.9 26.1 93.8 25.2 115.4 30.2


97

33rd COCOTLCII Meeting, July 15-l‘L I ‘>%. Kuala Lumpur, Malaysia

F i g u r e 8: M o i s t u r e d i s t r i b u t i o n in U P L B d r y e r

Table 5: Average temperature and sd in bottom layer of modified kukum dryer

avg.Temperatures

right middle left


front 99.2 8.9 104.4 9.8 97.5 8.4

middle 98.1 9.1 96.5 8.9 100.8 9.6

back 71.7 6.7 78.1 6.3 79.6 6.6


98

33rd COCOTliC II Meeting, July 15*19, 1996, Kuala Lumpur, Malaysia

0 10 20 30 40 50 60

time [h]

F i g u r e 9: D r y i n g c u r v e M o d i f i e d K u k u m d r y e r

T a b l e 6 : A d v a n t n e c s / D i s a d v a n t n g c . s o f d i f f e r e n t c c o m i t d r y e r s

T a p a h a n

d e V a p o r

T a p a h a n

D r y e r

M o d i f i e d

K u k u m

D r y e r

U P L B

D r y e r

C o c o p u g o n S o l a r / S u n

d r y e r

Q u a l i t y - - + - + +/-

L a b o r

r e q u i r e m e n t

- - - - + +

D u r a b i l i t y - - - - + -

M a i n t e n a n c e +/- +/- - - + +

C o n s t r u c t i o n - + + +

O p e r a t i o n - - - + + +

C o s t s ( D r y e r ) + + - - - +

C o s t s / k g c o p r a 0.025


99

33rd COCOTECI I Meeting, July 15-19. 1996, Kuala Lumpur. Malaysia

Figure 10: B r i c k d r y e r ( C o c o p u g o n )

Coconut Dryer und Drying Technologies

100


Figure 11: Temperature on burner surface and in bottom layer

100

90

80

CJoL— I

CJ

a aCJCL£~ 70CJCO2 CJ > a 60

50

Distance between drying bedand soil: 1.75 mTrial No.: 136 ’______

D ryer: C ocopugon

Fron t M iddle Back

Figure 12: T e m p e r a t u r e d i s t r i b u t i o n o f C o c o p u g o n


101

33rd COCOTliCI I Meeting, July 15-19. 1990, Kuala Lumpur. Malaysia

Table 7: Average temperature and standard deviation (sd) in bottom layer ol eoeopugon

avg.temperature

right middle left


front 73.9 3.1 77.1 3.4 77.1 3.2

middle 77.3 2.9 78.1 2.9 78.4 2.6

back 74.4 3.3 74.8 2.9 74.2 2.9

Particulars

Dryer cost (excluding shed) USS 970

estimated burncr/licat exchanger service life 5 years

estimated door service life 1 year

estimated chimney service life 10 years

cost of coconut husks USS 3.2/1000 PCs.

direct labor rate USS 0.64/hour

dryer load 2.500 nuts

COMPUTATIONS:

Direct Labor Cost [USS]

dryer loading = 0.14 min/nut x 2500 = 5.84 hrs. 3.7

dryer operation:a liring/fucling: 15 min x 8 times x 1 person =* 2 hrs 1.27b fuel prepuralion/hauling: 1.335 x 2 persons - 2.67 hrs. 1.70

dryer unloading: 1.67 hrs (2 or 3 persons) 1,06

Direct Muterial Cost

husks for fuel ( 80% of nuts loaded) = 2000 PCs. x USS 0.0032/pc 6.4

fixed Overhead Cost

Repairs and Maintenanceburncr/licat exchanger: US$ 169.8 (10%/ycar)/96 loads 0.18chimney: USS 99.6 (10%/ycar)/96 loads 0.10door US$43.1 (IO%/ycar)/96 loads 0.04

Depreciation: USS 970 ycars/96 drying loads every year @ 2 loads per week (full utilization) 2.02

TOTAL DRYING COST PER BATCH (USS) 16.5

Total copra produced 625 kg

Cost/kg copra USS 0.026

Note; 1 he computation only included the activities from loading to unloading since the other activities in copra making arc assumed the same for all the other dryers.


102

33rd COCOTECH Meeting, July 15-19, I ‘>96, Kuala Lumpur, Malaysia

Reflection Cover outside

Tronsmission Cover

Reflection Cover inside

Reflection Coconut

Heat Conduction

Solar Radiation

Figure 13: Working principle of solar dryer

Figure 14: Solar dryer for coconuts


33rd C0C0TEC11 Meeting, July 15-19, 1996, Kuala Lumpur, Malaysia

I able 9: Bill of materials [US$] for bamboo made solar dryer: (Size: 08" x 120")

u n it q u a n t i ty s u b to ta l

Bamboo poles "Tinik'V'Tunukon" pole 2 2.00

Nails (3 x 65) kg 0.25 0.25

Nails (3x80) 0.25 0.25

Woodglue (water resistent) 1 0.25 0.80

Gasoline 1 0.5 0.18

Sandpaper piece 2 0.80

Canvas strips m2 0.04 0.12

LDPE-plastic film UV-protected (0.125mm x 55")

m2 5.7 2.20

T o t a l 6 .6 0

Table 10: Assumptions Solar Drying:

Drying cycles/year 52 Working time (per 1000 nuts)

Drying capacity [nuts/sq.m.] 33 arranging 10

Deprivation time 2 loading/unloading 15

Maintenance/repair 0 labor cost [US$] 0.32

kg copra/nut 0.2

Table 11: Properties of LLD- and LD-Poly-Ethylene plastic sheets [10]

PE-type LLD LD

Melting point [°C] 120- 130 105-115

Molecular structure - linear branched

Gauge [-(mm)] 0.006 (0.15) 0.006 (0.15)

Tensile strength (lengthwise) [N/mm2] 33.1 22.3

Tensile strength (crosswise) [N/mm2] 34.7 19.7

Tear dilation (lengthwise) [%] 1360 510

Tear dilation (crosswise) [%] 760 1480


104


time [h]

CO

03T303

Figure 15: Radiation and tempature (meat, air and ambient) during solar drying

Figure 16: Drying curve solar and sun drying

Coconut Dryer and Drying Technologic*

105

1. Das, K. P.; The stale of art: Copra prodution in India. In: Coconuts Today/December 30, 1986. United Coconut Association of the Philippines, Inc. (UCAP), Manila, Philippines

2. Lozada, P.E.: The Los Banos Multi Crop Dryer. Philippine Coconut Research and Development Foundation, Inc.. Quezon City, Philippines, 1987.

3. Tung L., Hinay E.A. Copra Drying. 1. Comparison between the recommended pratice and fanners practice of splitted-nut arrangement before drying, hi: Annals of Tropical Research (Baybay, Philippines) Oct. 1979

4. Woodroof, I.G. Coconuts: Production, Processing. Westport, Connecticut: The AVI Publishing Co, hie.

5. Guarte, R.; Miihlbauer, W.; Kellert, M.: Influence of drying air jmrameters on the drying charateristics of copra and the qualtiy of copra and coconut oil. In: Postharvest Biology Technology.

6. E.P. Lozada; Jeremias, B. Benico; Vicente R. Hao Chin , Jr. : hi: The Aflatoxin Problem: The driving force to improve Productivity of the coconut Industry. Proceedings of the 2nd National Coconut week Symposium on “The coconut Farmers: A Look in to the future" PCA Auditorium, Diliman, Quzon City, 26 August 1988.

7. D. L. Dumaluan; E.P. Lozada: TheDrying characteristics of coconut meat. In: Philippine Agricultural Engineering Journal

8. KloBmann, H.: Influence of Direct Drying on the Quality of Copra and Coconut Oil. Thesis at the Institute of food technology, Fulda, 1995.

9. Brenndorfer, B; Kennedy L.; Oswin Bateman, C.O.; Trim, D.S.; Mrema, G.C.; Wereko-Brobby, C.: Solar Dryers - their role in post-harvest processing. Conunonwealth Science Council, Marlborough House, Pall Mall, London SW1Y 5HX. 1987.

10. Nentwig, J.: Kunststoff-Folien: Herstellung, Eigenscliaften, Anwendung. Hanser Verlag. Munich (Germany), 1994.

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